CN115176191B - Optical system comprising a light-guiding optical element having a two-dimensional extension - Google Patents

Abstract

An optical system includes an image redirecting arrangement having at least two reflectors to direct a collimated image from an image projector to propagate in first and second directions within a light guide optical element (LOE), the collimated image then being reflected by corresponding first and second sets of partially reflective inner surfaces toward an outcoupling optical arrangement. A portion of the field of view (FOV) adjacent to the right side of the collimated image propagating in the first direction intersects a plane of one of the sets of partially reflective inner surfaces or a plane parallel to the main outer surface, thereby forming a self-overlap of a portion of the collimated image in the field of view region that does not reach the user's eye.

Description

Optical system comprising a light-guiding optical element with two-dimensional expansion

Technical Field

The present invention relates to optical systems, and in particular, to optical systems comprising light-guide optical elements (LOEs) for achieving an optical aperture expansion.

Background

Many near-eye display systems include a transparent light guide optical element (LOE) or "waveguide" placed in front of the user's eye, which transmits the image within the LOE by internal reflection, and then couples the image out towards the user's eye by a suitable output coupling mechanism. The out-coupling mechanism may be based on embedded partial reflectors or "facets", or may employ diffractive elements. The following description will mainly relate to a facet-based out-coupling arrangement.

Various LOE configurations for achieving two-dimensional expansion of the optical aperture of an image projector are disclosed in commonly assigned us patent number 10,551,544 and PCT patent application publication number WO 2020/049542 A1 with the present application. In these examples, the first set of partially reflective facets progressively reflect an image injected into the LOE to redirect the image from a first direction to a second direction while achieving a first dimension of aperture expansion, and the second set of partially reflective facets progressively couple out of the redirected image while achieving a second dimension of aperture expansion.

When implementing such a configuration with a large field of view, the range of angles that can be used is limited at one end by the requirement that all rays of an image propagating within the LOE must be incident on a major surface of the LOE at incident angles greater than the critical angle. At the other end, if the angular field of the image within the LOE intersects the central plane of the LOE, some rays of the image overlap (i.e., in the same direction) as rays of the conjugate image, resulting in damage to that portion of the image. Because any portion of the image field that intersects the plane of the facet is damaged by reflection from adjacent areas of the image, additional limitations are imposed on the plane of the partially reflective surface ("facet") within the LOE. These considerations complicate the design of the LOE for two-dimensional aperture expansion and impose limits on the angular field of images that can be displayed.

Disclosure of Invention

The present invention is an optical system for directing image illumination to an eyebox for viewing by a user's eye.

According to teachings of embodiments of the present invention, an optical system for directing an image to an eye-box for viewing by a user's eye is provided, the optical system comprising (a) an image projector projecting illumination corresponding to a collimated image having an angular field of view from left to right and from top to bottom and a chief ray at the center of the field of view representing a direction of propagation, (b) a light guiding optical element (LOE) formed of a transparent material and having first and second major mutually parallel outer surfaces, (c) an image redirecting arrangement comprising at least a first reflector and a second reflector, the first reflector being arranged to redirect illuminated portions in a first direction within the LOE such that the collimated image propagates in the first direction by internal reflection, the second reflector being arranged to redirect illuminated portions in a second direction within the LOE such that the collimated image propagates in the second direction by internal reflection, (d) an outcoupling optical arrangement associated with the LOE and configured to cause the LOE to propagate in the second direction by internal reflection, the first group of mutually parallel reflective surfaces and the first group of mutually parallel groups of mutually reflective surfaces are arranged to mutually reflect off the first group of mutually parallel groups of surfaces, wherein the illuminated portion redirected in the first direction and redirected by the first set of partially reflective inner surfaces provides at least a left side of the field of view to the eye-box, and wherein a portion of the field of view adjacent to a right side of the collimated image propagating in the first direction intersects a plane of one of the sets of partially reflective inner surfaces or a plane parallel to the primary outer surface, thereby forming a self-overlap of a portion of the collimated image in a region of the field of view not reaching the eye-box.

According to another feature of an embodiment of the invention, the illuminated portion redirected in the second direction and redirected by the second set of partially reflective inner surfaces provides at least a right side of the field of view to the eyebox, and wherein a portion of the field of view adjacent to a left side of the collimated image propagating in the second direction intersects a plane of one of the sets of partially reflective inner surfaces or a plane parallel to the primary outer surface, thereby forming an auto-overlap of a portion of the collimated image in a region of the field of view not reaching the eyebox.

According to another feature of an embodiment of the present invention, the image redirection arrangement comprises a reflective prism external to the LOE, the reflective prism providing a first reflector and a second reflector.

According to another feature of an embodiment of the invention, the first reflector is a reflective surface inside the LOE and parallel to the first set of partially reflective inner surfaces, and the second reflector is a reflective surface inside the LOE and parallel to the second set of partially reflective inner surfaces.

According to another feature of an embodiment of the present invention, the first set of partially reflective inner surfaces and the second set of partially reflective inner surfaces are in overlapping relationship in at least one region of the LOE.

According to another feature of an embodiment of the present invention, the first set of partially reflective inner surfaces and the second set of partially reflective inner surfaces are each at an oblique angle to a major outer surface of the LOE.

According to another feature of an embodiment of the present invention, a portion of the field of view adjacent to the right side of the collimated image propagating along the first direction intersects the plane of the second set of partially reflective inner surfaces.

According to another feature of an embodiment of the present invention, a portion of the field of view adjacent to the right side of the collimated image propagating along the first direction intersects a plane parallel to the main outer surface.

According to another feature of an embodiment of the present invention, the out-coupling optical arrangement comprises a third set of mutually parallel partially reflective inner surfaces that are non-parallel to both the first set of partially reflective inner surfaces and the second set of partially reflective inner surfaces, the mutually parallel third set of partially reflective inner surfaces being at an oblique angle to the major outer surface of the LOE.

Drawings

The present disclosure is described herein, by way of example only, with reference to the accompanying drawings, in which:

FIGS. 1A and 1B are schematic isometric views of an optical system implemented using a light guide optical element (LOE) constructed and operative in accordance with the teachings of a first aspect of the present invention, showing top-down and lateral injection configurations, respectively;

FIG. 2A is a schematic isometric view showing a field of view (FOV) of an image viewed by a user's eye;

fig. 2B is a schematic top view showing the areas of the LOE that provide the left and right ends of the FOV to an Eye Motion Box (EMB);

FIG. 2C is a view similar to FIG. 2B, additionally showing the end of the field of view projected from the area of the LOE that does not reach the EMB, and thus allowing the end to be damaged in accordance with aspects of the invention;

FIG. 3A is a sequence of schematic representations of angular spaces showing a reflection sequence for providing alternative light paths to the right (top of the figure) and left (bottom of the figure) of the field of view;

Fig. 3B (1) and 3B (2) are schematic top views of the high quality portion and the damaged portion of the projected image from the right and left sides of the LOE, respectively, with only the high quality portion of the projected image reaching the EMB;

FIGS. 3C and 3D are a series of schematic front and side views, respectively, showing the optical path of FIG. 3A in physical space;

FIGS. 3E and 3F are three-dimensional angular representations of the reflection sequence shown in FIG. 3A, where FIG. 3E includes arrows showing the reflection sequence and FIG. 3F identifies the damaged areas of each image;

FIGS. 4A and 4B are three-dimensional angular representations similar to FIGS. 3E and 3F for an alternative embodiment of the present invention;

FIGS. 5A and 5B are three-dimensional angular representations similar to FIGS. 3E and 3F for another alternative embodiment of the present invention;

FIGS. 6-8 are schematic diagrams of respective components and overall assembly structures of three alternative implementations of an LOE according to teachings of embodiments of the present invention;

FIG. 9 is a graph showing the angular dependence of reflectivity of a partially reflective interior surface (facet) for an implementation of the invention, and also showing the angular extent of various images propagating within the LOE;

FIG. 10 is a schematic front view of an implementation of the LOE of FIGS. 1A-8, showing center-down injection of the coupled-in image;

FIG. 11A is a view similar to FIG. 10, showing an implementation in which the in-coupled image is implanted vertically;

FIGS. 11B and 11C are schematic cross-sectional views taken along line XI-XI of FIG. 11A, showing first and second implementations of an image redirection arrangement for coupling in projection images in two directions;

FIG. 12A is a view similar to FIG. 10, showing an implementation of upward injection of the in-coupling image;

FIGS. 12B and 12C are schematic cross-sectional views taken along line XII-XII of FIG. 12A, illustrating first and second implementations for coupling in a projection image in an upward direction;

FIG. 13A is a schematic angular representation of another implementation of the invention employing a first set of partially reflective inner surfaces and a second set of partially reflective inner surfaces perpendicular to the major outer surface of the LOE, and

Fig. 13B is a schematic front view of an LOE corresponding to the embodiment of fig. 13A.

Detailed Description

The present invention is an optical system for directing image illumination to an eyebox for viewing by a user's eye.

The principles and operation of an optical system according to the present invention may be better understood with reference to the drawings and the accompanying description.

By way of introduction, certain aspects of the present invention relate to optical systems for directing image illumination to an eye-box (EMB) for viewing by a user's eye via a light-guide optical element (LOE). The optical system provides an optical aperture expansion for the purpose of a heads-up display, and most preferably a near-eye display, which may be a virtual reality display or more preferably an augmented reality display. Preferably, the optical system provides a two-stage expansion of the input optical aperture, and wherein the first expansion is achieved using two different sets of mutually parallel partially reflective surfaces ("facets"), each set of partially reflective surfaces managing a different portion (not identical but preferably overlapping) of the overall field of view (FOV) presented to the eye.

In a typical but non-limiting embodiment (fig. 1A and 1B), the optical system employs a single image projector ("POD") that provides image illumination to two sets of facets integrated into the LOE. In summary, fig. 1A and 1B illustrate an optical system for directing illumination of an image injected into at least one in-coupling region to an eyebox for viewing by a user's eye. The optical system includes a light guide optical element (LOE) 112, the light guide optical element 112 being formed of a transparent material and including a first region 116, the first region 116 comprising a first set of planar, mutually parallel partially reflective surfaces ("facets") having a first orientation and a second set of planar, mutually parallel partially reflective surfaces ("facets") having a second orientation, the second orientation being non-parallel to the first orientation. (the facets are not visible in FIGS. 1A and 1B, but will be schematically shown in the following figures.) the LOE also includes a second region 118, the second region 118 containing a third set of planar, mutually parallel partially reflective surfaces (or "facets", also referred to as "outcoupling surfaces") having a third orientation that is non-parallel to each of the first and second orientations. The LOE is bounded by a set of mutually parallel major outer surfaces extending across the first and second regions such that the first, second and third sets of partially reflective surfaces are all located between the major outer surfaces.

The third set of partially reflective surfaces are at an oblique angle to the primary outer surface such that a portion of the image illumination propagating from the first region into the second region within the LOE by internal reflection at the primary outer surface couples out of the LOE toward the eyebox for viewing by the user's eye. Alternatively, instead of a third set of facets, a diffractive optical element may be used in the second region 118 for gradually coupling out the image illumination towards the eye-box. Similarly, a diffractive optical element may be used to couple the image illumination from projector 114 into the LOE to propagate within first region 116 by internal reflection.

Each partially reflective surface of the first and second sets of partially reflective surfaces is oriented such that a portion of the image illumination from the at least one incoupling region that propagates within the LOE by internal reflection at the primary outer surface is deflected toward the second region.

Most preferably, each of the first and second sets of facets is responsible for aperture expansion of a different portion of the entire field of view. In particular, preferably, the first set of partially reflective surfaces deflects a first portion of the field of view of the image toward the second region and the second set of partially reflective surfaces deflects a second portion of the field of view of the image toward the second region, the first and second portions of the field of view combining to provide a continuous combined field of view that is larger than each of the first and second portions of the FOV. Preferably, the two portions of the FOV correspond approximately to both sides of the full FOV (left and right or up and down, but are arbitrarily referred to hereinafter as "left" and "right"), but with sufficient overlap with the center area to ensure complete and continuous coverage of the center field across the eye-box, which corresponds to an acceptable range of positions of the viewer's pupil for which the display is designed.

The exemplary embodiment of the present invention takes the form of a near-eye display, generally designated 110, which employs an LOE 112. The compact image projector (or "POD") 114 is optically coupled to inject an image into the LOE 112 (interchangeably referred to as a "waveguide," "substrate," or "slab"), capturing image light in one dimension by internal reflection at a planar primary exterior surface within the LOE 112, light striking first and second sets of partially reflective surfaces (interchangeably referred to as "facets"), wherein each set of facets is tilted with respect to the direction of propagation of the image light, wherein each successive facet deflects a portion of the image light into a direction of deflection that is also captured/directed within the substrate by internal reflection.

The first and second sets of partially reflective surfaces located in region 116 deflect the image illumination from a first propagation direction that is captured within the substrate by total internal reflection (total internal reflection, TIR) to a second propagation direction that is also captured within the substrate by TIR. This partial reflection at successive facets achieves an optical aperture expansion in a first dimension.

The deflected image illumination then enters a second substrate region 118, which second substrate region 118 may be implemented as an adjacent different substrate or as a continuation of a single substrate, in which second substrate region 118 the out-coupling optics (another set of partially reflective facets or diffractive optical elements) progressively couple out a portion of the image illumination towards the eyes of an observer located within a region defined as an eye-box (EMB), thereby enabling an optical aperture expansion in a second dimension. The entire device may be implemented separately for each eye and preferably the entire device is supported relative to the user's head with each LOE 112 facing a respective eye of the user. In one particularly preferred option as shown herein, the support arrangement is implemented as an eyeglass frame having sides 120 for supporting the device relative to the user's ears. Other forms of support arrangements may also be used including, but not limited to, headbands, goggles, or devices that hang from a helmet.

Reference is made herein to the X-axis and the Y-axis in the drawings and claims, wherein the X-axis extends horizontally (fig. 1A) or vertically (fig. 1B) along the general direction of extension of the first region of the LOE, and the Y-axis extends perpendicular to the X-axis, i.e. vertically in fig. 1A and horizontally in fig. 1B.

In very similar terms, it can be said that the first region 116 of the LOE 112 achieves an aperture expansion in the X-direction, while the second LOE or the second region 118 of the LOE 112 achieves an aperture expansion in the Y-direction. The details of the expansion of the angular direction of propagation of the different parts of the field of view will be more precisely described below. It should be noted that the orientation as shown in fig. 1A may be considered a "top-down" implementation in which the image illumination into the main (second region) of the LOE enters from the upper edge, while the orientation as shown in fig. 1B may be considered a "lateral injection" implementation in which the axis, referred to herein as the Y-axis, is arranged horizontally. In the remaining figures, various features of certain embodiments of the present invention will be shown in the context of a "top-down" orientation similar to that of fig. 1A. However, it should be understood that all of these features are equally applicable to lateral implantation implementations and are within the scope of the present invention. In some cases, other intermediate orientations may also be suitable and are included within the scope of the present invention unless explicitly excluded. For simplicity and clarity of presentation, both sides of the display image provided by the different first and second sets of facets are referred to below as "left" and "right" corresponding to the ends in the X-direction, but as noted above, "left" and "right" do not necessarily correspond to the horizontal spacing in the final arrangement orientation of the device.

In a first set of preferred but non-limiting examples of the invention, the aforementioned first and second sets of facets are orthogonal to the major outer surface of the substrate. In this case, both the injected image and its conjugate, which undergoes internal reflection as it propagates within the region 116, are deflected and become a conjugate image that propagates in the direction of deflection. In an alternative set of preferred but non-limiting examples, the first set of partially reflective surfaces and the second set of partially reflective surfaces are at oblique angles relative to the major outer surface of the LOE. In the latter case, the injected image or conjugate thereof forms the desired deflected image propagating within the LOE, while the other reflection may be minimized, for example, by employing an angle-selective coating on the facets, wherein the angle-selective coating makes it relatively transparent to the range of incidence angles exhibited by images that do not require its reflection.

Preferably, the POD employed by the apparatus of the present invention is configured to generate a collimated image, i.e., wherein the light of each image pixel is a parallel beam collimated to infinity in an angular direction corresponding to the pixel location. Thus, the image illumination spans a range of angles corresponding to the two-dimensional angular field of view. This angular field of view is schematically represented in fig. 2A, where the user's eyes view the field of view, in this case a rectangle extending from the left "L" to the right "R" and from the upper edge "T" to the lower edge "B". The representative propagation direction is considered to be the central direction corresponding to the principal ray "C".

The image projector 114 comprises at least one light source, which is typically arranged to illuminate a spatial light modulator such as an LCOS chip. The spatial light modulator modulates the projection intensity of each pixel of the image, thereby generating an image. Alternatively, the image projector may comprise a scanning arrangement, typically implemented using one or more fast scanning mirrors, which scan the illumination from the laser light source across the image plane of the projector, while the intensity of the beam is changed synchronously from pixel to pixel with motion, so that the desired intensity is projected for each pixel. In both cases, collimation optics are provided to generate an output projection image that is collimated to infinity. Some or all of the above components are typically disposed on the surface of one or more polarizing beam-splitter (PBS) cubes or other prism arrangements known in the art.

The optical coupling of the image projector 114 to the LOE 112 may be achieved by any suitable optical coupling, for example, via a coupling prism having an angled input surface, or via a reflective coupling arrangement, via a side edge, and/or one of the major outer surfaces of the LOE. Alternatively, a diffractive optical element (DIFFRACTIVE OPTICAL ELEMENT, DOE) may be used to couple the image into the substrate. The details of the coupling-in configuration are generally not critical to the invention, except for those specified in some examples below, and are only schematically shown here.

It should be appreciated that the near-eye display 110 includes various additional components, typically including a controller 122 for actuating the image projector 114, typically employing power from a small on-board battery (not shown) or some other suitable power source. It should be appreciated that the controller 122 includes all the necessary electronic components, such as at least one processor or processing circuit, to drive the image projector, all of which are well known in the art.

Referring now to the top view of fig. 2B, it is noted that the right end of the projected image reaching EMB 4 originates from the region denoted "a" of LOE 2, while the left end of the projected image reaching EMB 4 originates from the region "B" of LOE. The EMB marks the range of eye positions required by the optical system to provide a complete FOV image. Aspects of the invention take advantage of this observation by allowing partial damage to the projected image in areas such as the area marked 6 in fig. 2C where the projected image does not reach EMB 4 and therefore does not affect the quality of the image viewed by the user.

Thus, in accordance with one aspect of the present invention, there is particular importance to the manner in which the image from projector 114 is redirected toward the first set of partially reflective surfaces and/or the second set of partially reflective surfaces. In particular, according to this aspect of the invention, the optical system further comprises an image redirecting arrangement comprising at least a first reflector and at least a second reflector, the first reflector being arranged to redirect a portion of the image illumination along a first direction within the LOE such that the collimated image propagates within the LOE by internal reflection along the first direction towards the first set of partially reflective inner surfaces, and the at least second reflector being arranged to redirect a portion of the illumination along a second direction within the LOE such that the collimated image propagates within the LOE by internal reflection along the second direction towards the second set of partially reflective inner surfaces. A portion of the field of view adjacent to the right side of the collimated image propagating in the first direction intersects a plane of one of the sets of partially reflective inner surfaces or a plane parallel to the main outer surface, thereby forming a self-overlap of a portion of the collimated image. However, since the first set of partially reflective surfaces provides the left side of the image to the eye-box, the self-overlap damages the image in the region of the view field that does not reach the eye-box.

Preferably, the opposite arrangement is used on the right side of the field of view. In particular, it is preferred that a portion of the field of view adjacent to the left side of the collimated image propagating in the second direction intersects a plane of one of the sets of partially reflective inner surfaces or a plane parallel to the main outer surface, thereby forming a self-overlap of a portion of the collimated image. However, since the second set of partially reflective surfaces provides the right side of the image to the eye-box, the self-overlap damages the image in the region of the view field that does not reach the eye-box. Specific examples of the redirection arrangement and its corresponding impact on certain areas of the image that do not reach the eye-box will be presented below.

Turning now to fig. 3A-3D, these figures schematically illustrate a two-dimensional aperture expansion of a large FOV in accordance with a non-limiting example of the present invention. Fig. 3A shows a process in an angular space, and fig. 3B (1) to 3D show equivalent processes in a real space.

The representation of fig. 3A is based on a two-dimensional rectilinear representation of angular space, wherein spherical coordinates are depicted in cartesian coordinates. The representation introduces various deformations and displacements along different axes are not exchangeable (as is the nature of rotations around different axes). However, this form of drawing has been found to simplify the description and provide a useful tool for system design. Circles represent the critical angle (boundary for Total Internal Reflection (TIR)) of the main outer surface of the waveguide. Thus, the points outside the circle represent the angular direction of the beam to be reflected by TIR, while the points inside the circle represent the beam to pass through the facet and to be transmitted out of the waveguide. Circle 9 represents the critical angle of the front and back surfaces of the waveguide. The "distance" between the circle centers is 180 degrees.

These figures show 4 successive stages of image illumination by the optical system after successive reflections. The initial state after the rectangular image 14 is injected into the waveguide is shown at stage 10. Since image 14 is located outside circle 9, its light rays are guided by TIR (hence represented as two coupled rectangles 14 and 14') as image 14 propagates along the waveguide by internal reflection at the main surface of the waveguide. This propagation of the image is represented as an arrow in the real space description of the waveguide 16 shown in stage 10 of fig. 3C. Throughout this document, the actual spatial propagation direction is shown with reference to the in-plane component of the propagation direction parallel to the main surface of the substrate. It should be understood that the arrows represent propagation by internal reflection reflected from the front and back surfaces of the waveguide and generally indicate the in-plane components of the chief rays of the image.

As the image propagates in the waveguide, a first reflector and a second reflector of the redirecting optical arrangement are encountered, which are depicted in angular space as dash-dot line 18A and dash-dot line 18B, respectively. These facets redirect the image in angular space, as shown by rectangles 15A and 15B, each of rectangles 15A and 15B generates its own conjugate image 15A 'and conjugate image 15B' by internal reflection at the major outer surface of the LOE. In real space (stage 11 of fig. 3C), the redirected image propagation direction is represented as laterally propagating arrows "a" and "B".

In this non-limiting example, the first reflector is a reflective surface inside the LOE and parallel to the first set of partially reflective interior surfaces, and the second reflector is a reflective surface inside the LOE and parallel to the second set of partially reflective interior surfaces. Specific examples of how such a structure may be implemented will be described below with reference to fig. 6 to 8.

It is apparent that facet plane 18A intersects one of the images 15A' at region 20. Thus, the portion of the image itself is reflected, making the segment of the image unusable. The unusable segments are shaded within the rectangular image. A similar process occurs in images redirected by facet 18B, where image 15B' intersects the facet and causes damage to region 20. Although in many cases multilayer dielectric coatings to achieve partially reflective surfaces are designed to have low reflectivity at high angles of incidence, the reflectivity at grazing incidence is always high, and thus such coatings cannot prevent damage to images intersecting the plane of the facets.

The deflected image is redirected to image 14 and image 14' by further reflections in the first set of facets and the second set of facets. Since all the guided images are coupled to each other, the unusable segments due to facet 18A are rendered to all four images, namely image 14, image 14', image 15A, and image 15A', and so on for the unusable segments generated by facet 18B. However, image 15A propagating on one side of the LOE has an opposite unusable segment, as shown in stage 12, compared to image 15B, which illustrates the coupling out of image 14' through the coupling out facet 22 to generate the coupled image 16A and the coupled image 16B. The top view (fig. 3B (1) and 3B (2)) shows how each sub-image (a and B) illuminates the eye-box 4 with an undamaged portion of its respective image, while an unusable portion of the image 6 is projected in a direction that is external to the eye-box and is therefore not visible to the user.

Fig. 3E and 3F illustrate the angular process described in fig. 3A in a three-dimensional angular representation. Here, the planes of facets 18 and 22 are shown as circles. Fig. 3E shows the same image shown in fig. 3A, while fig. 3F shows the generation of unusable portions as 20A1 and 20A2 folded over each other around facet 18, and the combined unusable portions propagated as 20B, 20C, 20D and coupled out as 20E.

Fig. 4A and 4B illustrate different angle architectures (in a non-limiting example of an image with a 4:3 form factor (ratio) and a 70 degree diagonal) according to an implementation of the invention. Here, however, the facet angle intersects the image angle distribution twice at 20A and at 20D. The two unusable portions overlap and thus the final result is equivalent to the results described above with reference to fig. 3A-3D.

Fig. 5A and 5B illustrate a case where the image 15 and the image 15' (the image deflected from the facet 18 and its conjugate) partially overlap to generate the unusable portion 20. This corresponds to the case where a portion of the field of view adjacent to the right (or left) side of the collimated image propagating in the first (or second) direction intersects a plane parallel to the main exterior surface. This causes the partial image to fold on itself. As in the previous example, this unusable portion only illuminates the region 6 (fig. 2B) outside the eye-box, while the eye-box 4 is illuminated by portions a and B of the image with undisturbed regions.

Fig. 6,7 and 8 depict various configurations of waveguides and corresponding components. For clarity of presentation, the dimensions are schematic. The actual size of each section is geometrically determined by the optical path required to reach the eye-box.

In fig. 6, the waveguide 31 is formed of four separate sections, a beam splitting section 30, which is composed of two overlapping sections 30A and sections 30B with facets inclined in different orientations. The orientation of the facets need not be tilted inversely or symmetrically, and thus, the redirected image illumination from the first reflector (18A) and the second reflector (18B) need not be in exactly opposite directions, and other considerations may be considered, such as tilting relative to the waveguide of the output image or different tailoring of the two images.

To improve image uniformity, a partial reflector (partial reflector, PR) may be introduced between overlapping portions parallel to the plane of the main outer surface of the waveguide.

Here, preferably, lateral portion 32 has facets parallel to portion 30A and portion 34 has facets parallel to portion 30B to perform image reflection toward second portion 36 of the LOE. As shown in stage 13 of fig. 3A and 3B, portion 36 is attached as a continuation to couple out light towards the eyes of the user. In this example, all of the sections are attached side by side, with section 30, section 32, and section 34 together constituting first waveguide section 116 of fig. 1A or 1B, and section 36 corresponding to second waveguide section 118.

Fig. 7 shows another alternative implementation in which the waveguide 50 is assembled from portions 52 overlying portions 54 to provide a first waveguide portion 116, the first waveguide portion 116 effecting a redirecting optical arrangement and beam splitting operations of the first and second sets of partially reflective surfaces. The portions 36 corresponding to the second waveguide portions 118 of fig. 1A or 1B are placed consecutively to couple out the image. Here, the Partial Reflector (PR) may also be implemented as a coating between overlapping portions (here, the lower portion 52 attached in opposing relation to the upper portion 54 is shown). In both cases of fig. 6 and 7, the components may alternatively be sandwiched between continuous glass cover plates to help achieve a high quality planar outer surface of the waveguide.

Fig. 8 shows another option according to which all parts (part 62, part 64 and part 66) are placed one on top of the other to assemble the waveguide 60. As shown, each section includes a set of facets that are implemented at least in the relevant region of the waveguide and optionally extend across the entire dimension of the waveguide. Partial reflectors may be implemented at one or both interfaces to enhance image uniformity.

Achieving dielectric coatings to provide the desired partial reflection characteristics for a wide angle spectrum and all colors can be challenging. In principle, a standard software package for designing a multilayer dielectric coating can provide the required reflectivity variation according to angle, and will generate a corresponding coating design. However, the more specific the requirements, the more complex and expensive the coating becomes, and/or more compromises may have to be made with respect to the desired properties. The present invention facilitates this aspect of the design because the angle corresponding to the image area that would be damaged anyway or would not contribute to the image visible from the EMB anyway does not need to meet the reflectivity requirements required for the remaining images.

For example, fig. 9 shows angular reflectivity 18A for a typical implementation of a multilayer dielectric coating for facet 18 of the implementation of fig. 5. The angular spectrum of nominal image 14 is described herein as line 14N, and the angular spectrum of image 15 is described herein as 15N. The folding of the image 15 upon itself may be represented herein as a partial overlap of 14N over 15N, and the overlap angle range is 20N (representation 20). Because the range 20N does not include a high quality image that will reach the eye-box, this region can be ignored (i.e., no constraint is imposed) during coating design. Thus, the actual range of reflectivity and transmissivity required for the coating of facet 18A is actually shorter, which corresponds to lines 14F and 15F. This greatly facilitates the design of a suitable coating.

This process of shortening the dynamic spectrum is applicable to all other configurations shown, making the implementation of facet coatings for large FOV more practical.

In the example discussed so far, the image illumination from the image projector 114 is coupled into the first region 116 of the LOE before reaching the first and second reflectors of the image redirection arrangement, and these reflectors are integrated with the first and second sets of partially reflective inner surfaces. The coupling in this case may be achieved by any conventional arrangement known in the art, such as coupling prisms with inclined surfaces, coupling-in reflectors or diffractive optical elements. Fig. 10 schematically shows the power distribution along the waveguide for this family of solutions. The full input intensity of the image illumination is injected downwardly (in any direction shown) into the waveguide as image 14. A portion of the light is coupled in lateral direction 15A and lateral direction 15B. Which in turn is coupled to the second waveguide section as light 70. Some of the injected light 14 continues as light 71 without being reflected at the facets. The light typically has a relatively high intensity and will therefore produce non-uniformities in the projected image. This non-uniformity may be mitigated by achieving high reflectivity at some or all of the facets in segments 30, 52, 54, 62 and 64 (fig. 6-8).

Fig. 11A presents an alternative optical structure in which the first and second reflectors of the image redirection arrangement are part of a coupling-in arrangement for coupling light from an image projector (not shown) into the waveguide. In this case, as indicated by circle 14 in fig. 11A, it is preferable that the image 14 from the image projector is injected perpendicular to the major surface of the LOE. Two non-limiting examples of implementations of the image redirection arrangement are shown in fig. 11B and 11C.

In fig. 11B, projector 114 has an exit pupil on reflecting prism 78. Light from projector 114 is split by prism 78 into two beams, beam 15A and beam 15B, beam 15A being coupled into one side of the waveguide and beam 15B being coupled into the other side. In this configuration, there is no high intensity center beam similar to beam 71 of FIG. 10.

Fig. 11C shows an alternative implementation in which a facet board 80A and facet board 80B are similar to 30A and 30B of fig. 6 but attached to the outside of the waveguide. As described above, the facets in these two portions deflect the light into the laterally propagating images 15A and 15B. Nor is a high intensity central beam generated.

The two images, image 15A and image 15B, are injected into the waveguide after reflection by the facets of prism 78 or facets of plates 80A and 80B. Preferably, during this implantation, they are also trimmed by the edges 79 of the coupling-in arrangement. This trimming is most important for shallow beams. However, especially for the optical architectures of the type shown in fig. 5A and 5B, these shallowest beams generally correspond to regions 20 that do not contribute in any way to the image portion reaching the EMB, so they can also be trimmed during the coupling-in phase without losing performance. This allows the aperture of the image projector 114 and the width of the reflectors 78 and 80 of the image redirection arrangement to be less than would be theoretically required to transmit all of the image field in both directions. This enables the use of smaller projectors 114 and more concentrated energy.

Another set of options is schematically shown in fig. 12A-12C. In this case, the high intensity input image beam 14 is deflected "upward", i.e., away from the second region of the LOE where the out-coupling occurs. This also avoids the formation of non-uniformities as discussed with reference to beam 71 of fig. 10. The resulting geometry is schematically shown in fig. 12A. Fig. 12B and 12C schematically illustrate two specific non-limiting example solutions for coupling an input image upwards. In the case of fig. 12B, the incoupling prism provides a properly oriented surface for incoupling an upwardly directed image, while in fig. 12C, the incoupling prism provides a reflective surface for similarly incoupling an image from a projector (not shown). In both cases, the first and second reflectors of the image redirection arrangement are implemented here as internal reflectors within the waveguide.

Finally, referring to fig. 13A and 13B, the principles of the present invention may also be applied to the case of facets perpendicular to the major outer surface of the substrate. Fig. 13A shows an example of a vertical facet 90A (corresponding to the inclined facet 18) in angular space, where the projection is polar, viewed along the direction of propagation of the output image 16, for clarity. Implant image 15 is folded over image 14 by vertical facet 90A. The overlapping of image 14 and image 15 generates ghost image portion 20. Fig. 13B shows the propagation of the same beam in real space. Here, 90B is a vertical facet having an equal but opposite inclination to facet 90A.

All of the above principles can also be applied to a "sideways" configuration, where the image is injected from a POD located laterally outside the viewing area and is spread vertically by the first set of facets and then spread horizontally by the second set of facets for coupling into the user's eyes. It should be appreciated that all of the above configurations and variations are also applicable to lateral injection configurations.

Throughout the above description, reference is made to the X-axis and the Y-axis as shown, wherein the X-axis is horizontal or vertical and corresponds to a first dimension of the optical aperture expansion, and the Y-axis is another principal axis corresponding to a second dimension of the expansion. In this context, X and Y may be defined in an orientation generally defined by the support device (e.g., the eyeglass frame of fig. 1A and 1B described above) relative to the orientation of the device when mounted on the head of the user. Other terms generally consistent with the definition of the X-axis include (a) at least one straight line bounding the eyebox, which may be used to define a direction parallel to the X-axis, (b) edges of the rectangular projected image generally parallel to the X-axis and the Y-axis, and (c) boundaries between the first region 16 and the second region 18 extending generally parallel to the X-axis.

It should be understood that the above description is intended by way of example only and that many other embodiments are possible within the scope of the invention as defined by the appended claims.

Claims (7)

1. An optical system for directing an image to an eyebox for viewing by an eye of a user, the optical system comprising:

An image projector that projects illumination corresponding to a collimated image having an angular field of view from left to right and top to bottom, and a chief ray at the center of the field of view representing a direction of propagation;

a light guide optical element, LOE, formed of a transparent material and having first and second major outer surfaces parallel to each other;

An image redirection arrangement comprising at least a first reflector arranged to redirect a portion of the illumination in a first direction within the LOE such that the collimated image propagates in the first direction by internal reflection within the LOE, and at least a second reflector arranged to redirect a portion of the illumination in a second direction within the LOE such that the collimated image propagates in the second direction by internal reflection within the LOE;

An out-coupling optical arrangement associated with the LOE and configured to deflect radiation propagating within the LOE outwardly toward the eyebox, and

A plurality of sets of partially reflective inner surfaces within the LOE, the plurality of sets of partially reflective inner surfaces comprising a first set of mutually parallel partially reflective inner surfaces arranged to redirect the illumination propagating along the first direction toward the out-coupling optical arrangement and a second set of mutually parallel partially reflective inner surfaces arranged non-parallel to the first set of partially reflective inner surfaces to redirect the illumination propagating along the second direction toward the out-coupling optical arrangement,

Wherein the out-coupling optical arrangement comprises a third set of mutually parallel partially reflective inner surfaces that are non-parallel to both the first and second mutually parallel set of partially reflective inner surfaces, the mutually parallel third set of partially reflective inner surfaces being at an oblique angle to the major outer surface of the LOE,

Wherein the first set of mutually parallel partially reflective inner surfaces, the second set of mutually parallel partially reflective inner surfaces, and the third set of mutually parallel partially reflective inner surfaces are each located between the first major outer surface and the second major outer surface,

Wherein the portion of the illumination redirected in the first direction and redirected by the first set of partially reflective inner surfaces provides at least a left side of the field of view to the eyebox, and wherein a portion of the field of view adjacent a right side of the collimated image propagating in the first direction intersects a plane of one of the sets of partially reflective inner surfaces or a plane parallel to the primary outer surface to form a self-overlap of a portion of the collimated image in a region of the field of view not reaching the eyebox, and

Wherein the first set of partially reflective inner surfaces and the second set of partially reflective inner surfaces are in overlapping relation in at least one region of the LOE, an

Wherein a partially reflector implemented as a coating is arranged between overlapping portions of the first set of partially reflective inner surfaces and the second set of partially reflective inner surfaces in the overlapping relationship.

2. The optical system of claim 1, wherein the portion of the illumination redirected along the second direction and redirected by the second set of partially reflective inner surfaces provides at least a right side of the field of view to the eye-box, and wherein a portion of the field of view adjacent to a left side of the collimated image propagating along the second direction intersects a plane of one of the sets of partially reflective inner surfaces or a plane parallel to the primary outer surface, thereby forming a self-overlap of a portion of the collimated image in a region of the field of view that does not reach the eye-box.

3. The optical system of claim 1, wherein the image redirecting arrangement comprises a reflective prism external to the LOE, the reflective prism providing the first and second reflectors.

4. The optical system of claim 1, wherein the first reflector is a reflective surface inside the LOE and parallel to the first set of partially reflective interior surfaces, and the second reflector is a reflective surface inside the LOE and parallel to the second set of partially reflective interior surfaces.

5. The optical system of claim 1, wherein the first and second sets of partially reflective inner surfaces are each at an oblique angle to the major outer surface of the LOE.

6. The optical system of claim 1, wherein a portion of the field of view adjacent to the right side of the collimated image propagating along the first direction intersects a plane of the second set of partially reflective inner surfaces.

7. The optical system of claim 1, wherein a portion of the field of view adjacent to a right side of the collimated image propagating along the first direction intersects the plane parallel to the main outer surface.